BS 939:2007

This standard BS 939:2007 Engineers' squares (including cylindrical and block squares). Specification is classified in these ICS categories:

• 17.040.30 Measuring instruments

This British Standard specifies requirements for engineers’ try squares (excluding adjustable squares), cylindrical squares and block squares of solid or open form.

Section 1 specifies general requirements applicable to all types of square.

Section 2 specifies requirements for engineers’ try squares in three grades of accuracy, AA, A and B, with inner lengths of blade from 50 mm up to and including 1 000 mm.

Section 3 specifies requirements for cylindrical squares in accuracy grade AA in sizes from 75 mm up to and including 750 mm.

Section 4 specifies requirements for solid form block squares in accuracy grades AA and A in sizes from 50 mm × 40 mm up to and including 1 000 mm × 1 000 mm.

Section 5 specifies requirements for open form block squares in accuracy grades A and B in sizes from 150 mm × 100 mm up to and including 600 mm × 400 mm.

NOTE While the standard provides for squares in various grades of accuracy, it should be noted that their accuracy in use is dependent upon the flatness of the surfaces on which they are used.